Electromagnetic braking device for continuous casting mold and method of continuous casting by using the same

ABSTRACT

In a magnetic brake apparatus for a continuous casting mold having a pair of first and second upper electromagnets  17 A and  17 B which are oppositely placed near the rear faces of the opposing side walls of the continuous casting mold  10 , and a pair of first and second lower electromagnets  21 A and  21 B which are oppositely placed thereunder, a static magnetic field being generated between each pair of electromagnets to stem the stream of the molten steel supplied to the casting mold by the static magnetic field, the apparatus has controlling units which independently control a current supplied to magnetic coils  16 A and  16 B being constituents of the first and second upper electromagnets and a current supplied to magnetic coils  20 A and  20 B being constituents of the first and second lower electromagnets.  
     The intensity of the magnetic field between the magnetic poles of the upper and lower electromagnets can, thereby, be readily and inexpensively varied during casting without restriction.

TECHNICAL FIELD

[0001] The present invention relates to magnetic or solenoid brakeapparatuses for continuous casting molds and continuous casting methodsusing the same. The present invention particularly relates to a magneticbrake apparatus for a continuous casting mold which is suitably appliedwhen a static magnetic field is generated in molten steel in a mold usedin continuous casting to control the flow of the molten steel, and to acontinuous casting method using the same.

BACKGROUND ART

[0002] In general, in continuous casting of slabs, molten steel reservedin a tundish is introduced into a continuous casting mold via ansub-entry nozzle connected to the bottom of the tundish, although nodrawing is shown. In this case, the flow rate of the molten steeldischarged from the discharging opening of the sub-entry nozzle issignificantly higher than the casting rate. Thus, when inclusions or/andbubbles in the molten steel are deeply penetrated and captured bysolidified shells, these inevitably cause defects of the product. Whenthe upward flow is dominant in the jet stream of the molten steel, therise of the mold meniscus promotes fluctuation of the melt surface,resulting in adverse effects on the slab quality and casting operation.

[0003] In order to avoid such a problem, for example, Japanese PatentLaid-Open No. 3-142049 discloses a continuous casting technology forpreventing the occurrence of the above-mentioned problem, in which astatic magnetic field is applied to the molten steel in the casting moldto brake the flow of the molten steel in the casting mold.

[0004]FIG. 6A is a cross-sectional view of a main portion of a castingapparatus disclosed in the above-mentioned patent, and FIG. 6B is anenlarged longitudinal cross-sectional view of a part of FIG. 6A. In thedrawings, numeral 101 represents a continuous casting mold comprising apair of short side walls 101A and a pair of long side walls 101B, itsinside being cooled by water. Numeral 102 represents an sub-entry nozzlefor supplying the molten steel from a tundish (not shown in the drawing)to the casting mold 101. Numerals 103A and 103B represent iron corebodies for forming a magnetic path. Numerals 104A, 104B, 105A and 105Brepresent upper and lower magnetic poles (iron cores) which areconnected to the iron core bodies 103A and 103B and extend along thewidth direction of the casting mold 101. Numeral 106 represents amagnetic field controlling means for controlling the intensity of thestatic magnetic field generated between the magnetic poles. The magneticfield controlling means 106 comprises a bracket 107 fixed to a support,a bracket 108 fixed to the iron core body 103B, a pivot pin connectingthe two brackets 107 and 108, and a hydraulic cylinder 110 fixed to thesupport in which the tip of the rod is engaged with the iron core body.Numeral 102B in the drawings represents a discharging opening of thesub-entry nozzle 102.

[0005] When the upper magnetic pole 104A at the left or A side in FIG.6A is; an N pole and the upper magnetic pole 104B at the B side is an Spole in the continuous casting mold 101, an A-to-B magnetic field isgenerated in the upper magnetic pole whereas a B-to-A magnetic field isgenerated in the lower magnetic pole. When molten steel is supplied intosuch a magnetic field, the upward flow is decelerated by the uppermagnetic field while the downward flow is decelerated by the lowermagnetic field. When the intensity of the static magnetic field ismodified between the upper magnetic pole and the lower magnetic pole inthe casting mold 101, the hydraulic cylinder 110 is operated by themagnetic field controlling means 106 so that the iron core body rotatesaround the pivot pin 109 to change the inter-pole distance of the uppermagnetic poles.

DISCLOSURE OF THE INVENTION

[0006] In the technology disclosed in the above-mentioned patent, aposition sensor for exactly adjusting the distance, in addition to thehydraulic: cylinder 110 and the pivot pin 109, is required. Thus, a widespace and many devices are required for a facility for adjusting theintensity of the static magnetic field. The patent also disclosesanother method for adjusting the magnetic field in which a nonmagneticmaterial is inserted in a part of the iron core. This method, however,has disadvantages, that is, the type, width of the slab and theintensity of the magnetic field in response to the casting speed cannotbe changed without limitation in the casting process. Since exchange ofthe nonmagnetic material requires long periods of time, operationefficiency is significantly low.

[0007] The present invention has been accomplished for solving theseproblems, and it is a first object to provide a technology which canreadily change the intensity of the magnetic field during castingwithout expensiveness and limitation.

[0008] It is a second object of the present invention to produce ahigh-quality cast product by achieving the first object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a cross-sectional view of a main portion whichillustrates an outlined configuration of an embodiment in accordancewith the present invention.

[0010]FIG. 2 is a schematic view of a combination of poles of magneticfields.

[0011]FIG. 3 is a line graph illustrating the quality of a slab preparedin an example.

[0012]FIG. 4 is another line graph illustrating the quality of a slabprepared in an example.

[0013]FIG. 5 is a cross-sectional view of a main portion whichillustrates an outlined configuration of another embodiment inaccordance with the present invention.

[0014]FIG. 6 is an outlined cross-sectional view of a conventionalcasting mold.

[0015]FIG. 7 is a cross-sectional view of a main portion whichillustrates an outlined configuration of another embodiment inaccordance with the present invention.

[0016]FIG. 8 is a schematic view of another combination of poles ofmagnetic fields.

[0017]FIG. 9 is a schematic view of another combination of poles ofmagnetic fields.

REFERENCE NUMERALS

[0018]10 continuous casting mold

[0019]12 sub-entry nozzle

[0020]14A upper iron core at the free side

[0021]14B upper iron core at the fixed side

[0022]16A upper coil at the free side

[0023]16B upper coil at the fixed side

[0024]17A first upper electromagnet

[0025]17B second upper electromagnet

[0026]18A lower iron core at, the free side

[0027]18B lower iron core at the fixed side

[0028]20A lower coil at the free side

[0029]20B lower coil at the fixed side

[0030]21A first lower electromagnet

[0031]21B second lower electromagnet

[0032]22A connecting iron core

[0033]22B connecting iron core

[0034]24A current controlling unit

[0035]24B current controlling unit

[0036]24C current controlling unit

[0037]24D current controlling unit

[0038] Sm molten steel

BEST MODE FOR CARRYING OUT THE INVENTIOIN

[0039] The embodiments of the present invention will now be described indetail with reference to the drawings.

[0040]FIGS. 1 and 7 are cross-sectional views of a main portionillustrating outlined configurations of embodiments in accordance withthe present invention. The magnetic brake apparatus in these embodimentsin accordance with the present invention is applied to a continuouscasting mold shown by reference numeral 10 in the drawings. Thecontinuous casting mold 10 is substantially the same as that shown inFIG. 6. Cooling water circulates through the interior of the side wall,and molten steel Sm is supplied to the continuous casting mold 10through a discharging opening (not shown in the drawings) of ansub-entry nozzle 12. The magnetic brake apparatus in these embodimentshas a first upper electromagnet 17A comprising an upper iron core 14Awhich is placed near the rear face of the side wall of the continuouscasting mold 10 at the free side (the left side in the drawings) andlies slightly above the discharging opening of the sub-entry nozzle 12,and an upper magnetic coil 16A wound around the electromagnet; and asecond upper electromagnet 17B at the fixed side (the right side in thedrawings) in the position of the same height comprising an upper ironcore 14B and an upper magnetic coil 16B. The first and second upperelectromagnets 17A and 17B are oppositely placed with the continuouscasting mold 10 intervening therebetween.

[0041] In FIG. 1, a first lower electromagnet 21A at the free sidecomprising a lower iron core 18A and a lower magnetic coil 20A, and asecond lower electromagnet 21B at the fixed side comprising a lower ironcore 18B and a lower magnetic coil 20B are provided below the upperelectromagnet. These two electromagnets 21A and 21B are also oppositelyplaced. The upper iron cores 14A and 14B and the lower iron cores 18Aand 18B are integrally formed with connecting iron cores 22A and 22Bprovided therebetween, and are magnetically connected to each other. Inthis embodiment, a current is supplied to these two upper magnetic coils16A and 16B being constituents of the first and second upperelectromagnets through an upper current controlling unit 24A, andindependently, a current is supplied to these two lower magnetic coils20A and 20B being constituents of the first and second lowerelectromagnets through a lower current controlling unit 24B. Thesecurrents are independently controllable.

[0042] That is, a current of a given ampere is applied to the two uppermagnetic coils 16A and 16B, whereas a current of another ampere isapplied to the two lower magnetic coils 20A and 20B. The intensities ofthe static magnetic fields between the upper electromagnets 17A and 17Band between the lower electromagnets 21A and 21B are independentlyadjustable.

[0043] In FIG. 7, a first lower electromagnet 21A at the free sidecomprising a lower iron core 18A and a lower magnetic coil 20A and asecond lower electromagnet 21B at the fixed side comprising a lower ironcore 18B and a lower magnetic coil 20B are provided below the upperelectromagnets. These two electromagnets are also oppositely placed. Theupper iron cores 14A and 14B and the lower iron cores 18A and 18B areintegrally formed with connecting iron cores 22A and 22B providedtherebetween and are magnetically connected to each other. Differentcurrents are independently supplied to the four magnetic coils 16A, 16B,20A and 20B through current controlling units 24A to 24D.

[0044] The operation of the embodiments will now be described.

[0045] In FIG. 1, when normal static magnetic fields are generated atthe upper and lower portions, two current controlling units 24A and 24Bindependently control the currents for the upper electromagnets 17A and17B and the lower electromagnets 21A and 21B. Thus, as shown in therelationship of the magnetic poles of the upper and lower electromagnetsin FIG. 2, when the upper magnetic pole at the free side is an S pole,the opposing upper magnetic pole at the fixed side is an N pole, thelower magnetic pole at the free side is an N pole, and the lowermagnetic pole at the fixed side is an S pole. That is, poles opposingeach other across the molten steel and the upper and lower poles on thesame side are different from each other. In this embodiment, in order toprevent capture of mold powder at the meniscus section of the moltensteel, the upper magnetic field may be enhanced to moderate thefluctuation of the molten surface. In order to prevent penetration ofnonmetallic inclusions into the deep interior of the molten steel, thelower magnetic field may be lowered to suppress the downward flow of themolten steel in the casting mold. The upper and lower electromagnets canappropriately control the intensities of the magnetic fields toadequately control the flow of the molten steel depending on thepurposes.

[0046] Thus, the quality of the cast slab is improved by casting whileadequately controlling the intensities of the static magnetic fields bythe upper and lower electromagnets in response to the width and type ofthe slab and the casting speed using the magnetic brake apparatus ofthis embodiment.

[0047] In FIG. 7, when normal static magnetic fields are generated atthe upper and lower portions, the four current controlling units 24A to24D independently control the currents for the correspondingelectromagnets. Thus, as shown in the relationship of the magnetic polesof the upper and lower electromagnets in FIG. 2, poles opposing eachother across the molten steel and the upper and lower poles on the sameside are different from each other. In this case, the most effectiveresults are achieved when the currents of the magnetic coils for theopposing poles are the same. In order to prevent capture of mold powderat the meniscus section of the molten steel, the upper magnetic fieldmay be enhanced to moderate the fluctuation of the molten surface. Inorder to prevent penetration of nonmetallic inclusions into the deepinterior of the molten steel, the lower magnetic field may be lowered tosuppress the downward flow of the molten steel in the casting mold.

[0048] In conventional apparatuses, it is impossible to make theintensity of the upper or lower magnetic field zero even when thecurrent to the magnetic coil is zero, because the upper and lower ironcores are magnetically connected to each other through the connectingiron core. In contrast, in this embodiment, the direction of the currentof one magnetic coil between the two opposing electrodes is inverted bythe current controlling units 24A to 24D so that the opposing magneticpoles are the same as shown in FIGS. 8 and 9. The intensity of themagnetic field thereby becomes zero.

[0049] Thus, in order to prevent inclusion of non-metallic impuritiesinto the solid shell at the meniscus section for the purpose of securingthe quality below the skin rather than capture of powder by thefluctuation of the molten surface, or in order to prevent capture ofbubbles of argon gas blown into the steel so that the dischargingopening of the sub-entry nozzle is not clogged, a magnetic field of zerobetween the upper electromagnets is effective when the flow of themolten steel is required at the meniscus section. This embodiment canreadily perform such a control.

EXAMPLE

[0050] An example of the embodiment will now be described.

[0051] Continuous casting was performed under the following conditionsusing a mold having a magnetic brake apparatus in accordance with theembodiment shown in FIG. 1 or 7 to produce a cast slab of low-carbonaluminum-killed steel. Its surface and internal quality was examined.FIG. 3 shows the results when the intensity of the lower magnetic fieldwas fixed to 2,400 gauss while the intensity of the upper magnetic fieldwas varied. On the other hand, FIG. 4 shows the results when theintensity of the upper magnetic field was fixed to 2,500 gauss. [CastingConditions] Casting speed: 2.5 m/min Width of slab: 1,400 mm Thicknessof slab 220 mm

[0052] Intensity of lower magnetic field: 2,000 to 3,000 gauss

[0053] Intensity of upper magnetic field: 2,000 to 3,000 gauss

[0054] The results shown in FIGS. 3 and 4 illustrate that adjustment ofthe intensity of the magnetic field in response to the operationalconditions is significantly effective.

[0055] As described above, since the flow of the molten steel can beappropriately controlled in the casting mold in this embodiment,inclusion of non-metallic impurities into the molten steel pool by thejet stream of the molten steel and capture of mold powder into themolten steel by the fluctuation of the molten surface at the meniscussection are prevented. Accordingly, a high-quality slab can be producedwith high efficiency.

[0056] Another embodiment in accordance with the present invention willnow be described.

[0057]FIG. 5 is a cross-sectional view, which corresponds to FIG. 1, ofan outlined configuration of a magnetic brake apparatus in accordancewith the present invention. The magnetic brake apparatus in thisembodiment has no connecting iron cores 22A and 22B, shown in FIG. 1,for magnetically connecting the upper and lower iron cores at the freeand fixed sides, and thus upper and lower iron cores 14A, 14B, 18A and18B are magnetically independent of each other. Other configurations aresubstantially the same as those in the first embodiment.

[0058] Since the upper and lower iron cores at the same side are notmagnetically connected to each other in this embodiment, the inputcurrent generates a magnetic field with a lower intensity than that inthe above-mentioned embodiment. Similar control can, however, beperformed and the static magnetic field of either the upper or lowerelectromagnet: can be set to be near zero.

[0059] Although the present invention has been described in detail, thepresent invention is not limited to the above-mentioned embodiments andincludes various modifications within a scope without departing from thegist of the present invention.

INDUSTRIAL APPLICABILITY

[0060] According to the present invention as described above, theintensity of the magnetic field between the magnetic poles of the upperand lower electromagnets can be readily and inexpensively varied duringcasting without restriction.

1. A magnetic brake apparatus for a continuous casting mold comprising:a pair of upper electromagnets oppositely placed near the rear faces ofthe opposing side walls of the continuous casting mold, and a pair oflower electromagnets placed thereunder; a static magnetic field beinggenerated between these paired electromagnets to stem the flow of themolten steel supplied to the continuous casting mold by means of thestatic magnetic field; wherein the magnetic brake apparatus furthercomprises controlling means for independently controlling currentssupplied to magnetic coils which are constituents of the electromagnets.2. A magnetic brake apparatus for a continuous casting mold according toclaim 1, wherein the magnetic brake apparatus has controlling means forindependently controlling the current supplied to the magnetic coilbeing a constituent of the pair of upper coils and the current suppliedto the magnetic coil being a constituent of the pair of lower coils. 3.A magnetic brake apparatus for a continuous casting mold according toeither claim 1 or 2, wherein an upper iron core and a lower iron corewhich are constituents of the upper electromagnet and the lowerelectromagnet, respectively, placed near the rear face at the same sideof the opposing side walls of the casting mold are magneticallyconnected to each other.
 4. A continuous casting method comprisingcontinuously casting while stemming the jet stream of the molten steelsupplied to the interior of the casting mold through a dischargingopening of an sub-entry nozzle using a magnetic brake apparatus for acontinuous casting mold according to go any one of claims 1 to 3.